The inflammatory response is one of the body's most important defenses against infection. One initiator of inflammation is bacterial lipopolysaccharide (LPS). We found some years ago that LPS will induce in macrophages 3 microRNAs. These are small RNAs that can have huge regulatory influences on protein levels. We have therefore been characterizing these 3 RNAs from various points of view and this request is for funds to study these RNAs in depth. One of the microRNAs has been linked to cancer induction and may provide a link between inflammation and cancer. We have also included plans to study another microRNA family because of its potential relationship to immune cell maturation. The planned studies take advantage of today's ability to manipulate the genetics of mice. Thus, overexpression and knockout studies will allow us to examine the consequences to mouse physiology of too much or none of the particular microRNAs. The overexpression studies will be done by incorporating into viral vectors genes that express the microRNAs, infecting bone marrow stem cells with these vectors and transferring the infected cells to lethally irradiated host mice. We will use high resolution surface marker analysis to characterize the role of these microRNAs in the generation and behavior of particular subsets of immune cells. In this work, we will also use in vitro expression in cells through vectored delivery of genes to the cells. MicroRNAs are processed from precursors and we have found that the processing itself is regulated. We plan to examine how this regulation is achieved. To understand how these microRNAs work we will characterize the target genes that they regulate. This involves bioformatics to find candidates, determining the genes whose expression is sensitive to a particular microRNA and then study of the role of those genes. For the microRNA family that may be involved in immune cell development, we suspect that it could be controlling the final stage of differentiation of the cells that make antibodies. We will therefore concentrate on examining that stage of immune cell development with an emphasis on the possible role of a protein usually associated with protecting the genome, p53. PUBLIC HEALTH RELEVANCE: Scientists have long thought that the immune system is controlled by proteins. Our recent work has implicated some small RNA molecules as controllers of inflammatory and immune responses. We plan to examine how such RNAs might work with an emphasis on the relationship between cancer and inflammation. Microbial infections and cancer are among the leading causes of human diseases worldwide. Therefore, it is imperative that we continue to define the molecular basis underlying these devastating problems. Very recently, micro-RNAs have emerged as a novel class of gene expression regulators that are implicated in both immune system regulation and cancer biology. Our group has found that a small number of miRNAs are potently induced by the innate immune response to infection, and therefore propose to characterize the roles of these miRNAs in host defense against infection and tumorigenesis